Currently employed medical imaging diagnostic apparatuses include CT (Computed Tomography) scanners, MRI (Magnetic Resonance Imaging) apparatuses, PET (Positron Emission Tomography) apparatuses, angiography apparatuses, and MRA (MR Angiography) apparatuses and the like. In using the abovementioned apparatuses to obtain diagnostic images of a patient, a chemical liquid such as a contrast medium or physiological saline is often injected into the patient.
Typically, the injection of the chemical liquid into the patient is automatically performed by using a chemical liquid injector. The chemical liquid injector has an injection head on which a syringe is removably mounted, and an injection control unit controlling the operation of the injection head. The syringe has a cylinder and a piston inserted into the cylinder to be movable forward and rearward. The chemical liquid is filled into the cylinder.
The injection head has a syringe fixing mechanism removably fixing the syringe and a piston driving mechanism moving the piston while the cylinder is fixed to the injection head. An injection needle or a catheter is connected to the leading end of the cylinder through an extension tube, the injection needle or the catheter is placed or inserted into a blood vessel of the patient, and then the piston is pushed into the cylinder by the piston driving mechanism to allow the injection of the chemical liquid filled in the syringe into the patient.
The obtaining of CT images using the contrast medium is desirably performed at a timing when the contrast medium reaches a region for imaging after the contrast medium is injected and flows with the bloodstream of the patient. Representative methods of determining the imaging timing include a test injection method and a bolus tracking method.
The test injection method involves injecting small amounts of contrast medium and physiological saline prior to main scan to perform imaging of the same section as in the main scan, checking the time for the contrast medium to reach a region of interest, and predicting a contrast medium reaching time in the main scan to set the imaging timing (see Patent Document 1).
The bolus tracking method involves monitoring real-time changes in CT value in an appropriate region after the injection of the contrast medium with pre-scan at an X-ray dose lower than in main scan and starting the main scan when the CT value exceeds a predetermined threshold value (see Patent Document 2).